In the composite manufacturing industry it is common place to impregnate mats of reinforcing material, such as glass or carbon fibers, with a resinous matrix material and form the impregnated mat into a final complex shaped product by compression molding, or any other suitable means.
Various mat structures are used depending upon end use of the product manufactured. Typical are chopped strand mats, continuos strand mats having various strand patterns, woven fabric mats, and/or braided fabric mats. Braided fabric mats may comprise biaxial or triaxial braided fiber bundles or yarns. Each bundle, or yarn, comprising hundreds or thousands of continuos, parallel, fibers therein.
Biaxial braided fabrics basically comprise a cross weave of fibrous yarns wherein a matrix of parallel yarns are interwoven into an orthogonal matrix of parallel yarns thereby forming a braided fabric. A triaxial braided fabric basically comprises a biaxial braided fabric having an additional matrix of parallel yarns extending the longitudinal, or axial, length of the braided fabric and interwoven into the biaxial braided yarns.
In the manufacture of composite products the reinforcing fibrous mats are generally manufactured off-site and shipped to the composite manufacturer upon large shipping rolls having numerous concentric layers of reinforcing mat from which the composite manufacturer simply unrolls sheets of the reinforcing mat as needed. The mats are impregnated with resin, placed in a mold, such as a compression mold, and formed into the desired product.
Concave and/or convex products such as composite bathtubs and/or automobile body parts are typically manufactured in such a manner using chopped strand and/or woven fibrous mats while braided mats are generally used for manufacture of composite products serving a more structural function.
Chopped strand, woven, and biaxial braided mats will generally conform to a concave or convex configuration; however, triaxial braided mats formed on a cylindrical braiding spool will not conform to a convex or concave configured mold without characteristic buckling of the axial yarns because the axial yarns are of equal axial lengths.
Triaxial braided fabrics generally find use in reinforcement of cylindrical composite products such as large diameter pipe where the axial yarns extend parallel to the pipe centerline thereby providing tensile strength in the axial direction with the biaxially braided yarns wrapping around the circumference of the pipe providing burst strength. For example see U.S. Pat. No. 5,899,134.
However, it is sometimes desirable to wrap a triaxially braided fabric circumferentially about a cylindrical product with the axial yarns wrapping circumferentially about the cylinder providing hoop type reinforcement.
However, if the end product is not truly cylindrical and has an axially varying diameter, such as a aircraft turbine engine cowling, a triaxial braided fabric will form an undesirable buckle in areas where the end product diameter varies. Normally, in such constructions, the triaxial braided reinforcing fabric would have to be braided directly upon the manufacturing mold thereby avoiding buckling of the axial yarns. Thus off site preparation of the triaxial braided reinforcing fabric is not suitable.
Thus a method is needed whereby a triaxial braided reinforcing fabric having variable length axial yarns may be manufactured off site, and wrapped upon a generally cylindrical shipping spool that will accommodate the variable length axial yarns of the triaxially braided fabric and delivered to the end user.